1. Field of the Invention
The present disclosure relates, in various embodiments, to golfballs. In particular, the present disclosure relates to a golfball having a liquid core and a cover layer comprising a reaction-injection-molded (RIM) material.
2. Description of the Related Art
Spin rate is an important golfball characteristic for both the skilled and unskilled golfer. High spin rates allow for the more skilled golfer, such as PGA professionals and low handicap players, to maximize control of the golfball. This is particularly beneficial to the more skilled golfer when hitting an approach shot to a green. The ability to intentionally produce “back spin”, thereby stopping the ball quickly on the green, and/or “side spin” to draw or fade the ball, substantially improves the golfer's control over the ball. Thus, the more skilled golfer generally prefers a golfball exhibiting high spin rate properties.
A high spin golfball, however, is not desirous by all golfers, particularly high handicap players who cannot intentionally control the spin of the ball. In this regard, less skilled golfers, have, among others, two substantial obstacles to improving their game: slicing and hooking. When a club head meets a ball, an unintentional side spin is often imparted which sends the ball off its intended course. The side spin reduces one's control over the ball as well as the distance the ball will travel. As a result, unwanted strokes are added to the game.
Consequently, while the more skilled golfer desires a high spin golfball, a more efficient ball for the less skilled player is a golfball that exhibits low spin properties. A low spin ball reduces slicing and hooking and enhances roll distance for the amateur golfer.
The present disclosure relates to the need for developing a golfball having a reduced spin rate after club impact, while at the same time maintaining durability, playability and resiliency characteristics necessary for repetitive play.
In this regard, top-grade golfballs sold in the United States maybe generally classified as one of three types: two-piece, three-piece balls, or multi-layer golfballs. The two-piece ball consists of a solid polymeric core and a separately formed outer cover. The so-called three-piece balls or wound balls consist of a liquid or solid center, elastomeric thread windings about the center, and a cover. A multi-layer golfball is a solid, non-wound golfball comprising one or more core, intermediate and/or cover layers.
Two-piece golfballs are produced by molding a natural (balata) or synthetic (i.e. thermoplastic resin such as an ionomer resin) polymeric cover composition around a preformed polybutadiene (rubber) core. During the molding process, the desired dimple pattern is molded into the cover material. In order to reduce the number of coating steps involved in the finishing of the golf balls, a color pigment or dye and, in many instances, an optical brightener are added directly to the generally “off white” colored polymeric cover composition prior to molding.
With respect to multi-layered golfballs, one or more intermediate or cover layers are molded around a generally solid core. Optionally, one or more core layers may also be included in the molded core. Depending upon the two-piece or multi-layer ball construction, the balls vary distinctly in such properties as playability (i.e. spin rate, compression, feel, etc.), travel distance (initial velocity, C.O.R., etc.), durability (impact, cut and weather resistance) and appearance (i.e. whiteness, reflectance, yellowness, etc.). This varies depending upon the ball's core, intermediate and cover layers, coating materials, as well as the ball's surface configuration (i.e. dimple pattern). Consequently, two-piece and multi-layer golfballs offer both the amateur and professional golfer a variety of performance characteristics to suit an individual's game.
In regard to the specific components of a golfball, although the nature of the cover can, in certain instances, make a significant contribution to the overall feel, spin (control), coefficient of restitution (C.O.R.) and initial velocity of a ball (see, for example, U.S. Pat. No. 3,819,768 to Molitor), the initial velocity of two-piece, three-piece, and multi-layer balls is determined mainly by the coefficient of restitution of the core. The coefficient of restitution of the core of wound (i.e. three-piece) balls can be controlled within limits by regulating the winding tension and the thread and center composition. With respect to two-piece and multi-layer balls, the coefficient of restitution of the core is a function of the properties of the elastomer composition from which it is made.
The cover component of a golfball is particularly influential in effecting the compression (feel), spin rates (control), distance (C.O.R.), and durability (i.e. impact resistance, etc.) of the resulting ball. Various cover compositions have been developed in order to optimize the desired properties of the resulting golfballs.
Over the last several years, improvements in cover, intermediate and core material formulations and changes in dimple patterns have more or less continually improved golfball distance. Top-grade golfballs, however, must meet several other important design criteria. To successfully compete in today's golfball market, a golfball should be resistant to cutting and must be finished well; it should hold a line in putting and should have good click and feel. In addition, the ball should exhibit spin and control properties dictated by the skill and experience of the end user.
Prior artisans have attempted to incorporate metal layers or metal filler particles in golf balls to alter the physical characteristics and performance of the balls. For example, U.S. Pat. No. 3,031,194 to Strayer is directed to the use of a spherical inner metal layer that is bonded or otherwise adhered to a resilient inner constituent within the ball. The ball utilizes a liquid filled core. U.S. Pat. No. 4,863,167 to Matsuki, et al. describes golfballs containing a gravity filler which may be formed from one or more metals disposed within a solid rubber-based core. U.S. Pat. Nos. 4,886,275 and 4,995,613, both to Walker, disclose golfballs having a dense metal-containing core. U.S. Pat. No. 4,943,055 to Corley is directed to a weighted warm-up ball having a metal center.
Prior artisans have also described golfballs having one or more interior layers formed from a metal, and which feature a hollow center. Davis disclosed a golfball comprising a spherical steel shell having a hollow air-filled center in U.S. Pat. No. 697,816. Kempshall received numerous patents directed to golfballs having metal inner layers and hollow interiors, such as U.S. Pat. Nos. 704,748; 704,838; 713,772; and 739,753. In U.S. Pat. Nos. 1,182,604 and 1,182,605, Wadsworth described golfballs utilizing concentric spherical shells formed from tempered steel. U.S. Pat. No. 1,568,514 to Lewis describes several embodiments for a golfball, one of which utilizes multiple steel shells disposed within the ball, and which provide a hollow center for the ball.
Prior artisans have attempted to provide golfballs having liquid filled centers. Toland described a golfball having a liquid core in U.S. Pat. No. 4,805,914. Toland describes improved performance by removing dissolved gases present in the liquid to decrease the degree of compressibility of the liquid core. U.S. Pat. No. 5,037,104 to Watanabe, et al. and U.S. Pat. No. 5,194,191 to Nomura, et al. disclose thread wound golfballs having liquid cores. Similarly, U.S. Pat. No. 5,421,580 to Sugimoto, et al. and U.S. Pat. No. 5,511,791 to Ebisuno, et al. are both directed to thread wound golfballs having liquid cores limited to a particular range of viscosities or diameters. Moreover, Molitor, et al. described golfballs with liquid centers in U.S. Pat. Nos. 5,150,906 and 5,480,155.
Two U.S. patents disclosing a golfball having a metal mantle layer in combination with a liquid core are U.S. Pat. No. 3,031,194 to Strayer and the previously noted U.S. Pat. No. 1,568,514 to Lewis. Unfortunately, the ball constructions and design teachings disclosed in these patents involve a large number of layers of different materials, relatively complicated or intricate manufacturing requirements, and/or utilize materials that have long been considered unacceptable for the present golfball market.
Concerning attempts to provide golfballs with cellular or foamed polymeric materials utilized as a core, few approaches have been proposed. U.S. Pat. No. 4,839,116 to Puckett, et al. discloses a short distance golfball. It is believed that artisans considered the use of foam or a cellular material undesirable in a golfball, perhaps from a believed loss or decrease in the coefficient of restitution of a ball utilizing a cellular core.
Although satisfactory in at least some respects, all of the foregoing ball constructions, particularly the few utilizing a metal shell and a liquid core, are deficient. This is most evident when considered in view of the stringent demands of the current golf industry. Moreover, the few disclosures of a golfball comprising a cellular or foam material do not motivate one to employ a cellular material in a regulation golfball. Specifically, there is a need for a golfball that exhibits a high initial velocity or coefficient of restitution (C.O.R), may be driven relatively long distances in regulation play, and which may be readily and inexpensively manufactured.
In an alternative embodiment, the spin rate of the ball is further reduced by increasing the thickness of the cover and/or decreasing the weight and softness of the core. By increasing the cover thickness and/or the overall diameter of the resulting molded golfball, enhanced reduction in spin rate is observed.
However, notwithstanding the enhanced cover thickness and/or diameters of these golf balls, it is still desirable to produce a U.S.G.A. regulation golfball having improved low spin properties while maintaining the resilience and durability characteristics necessary for repetitive play.
In golfballs with liquid cores, ball properties such as initial spin rate and spin decay, which affect the flight of the ball, are affected by the fluid dynamics of the liquid core. When struck, the liquid and the cover layer(s) spin at different rates. Over time, the spin rate of the ball drops (decays) as rotational kinetic energy from the spinning ball is transferred to the liquid until the fluid and the ball spin at the same rotational speed.
It is further desirable to provide a golfball having a liquid core and a construction that promotes favorable spin characteristics with both woods and irons. It is also desirable to provide a golfball having variable spin characteristics. Additionally, it is desirable to provide a golfball that exhibits a large spin decay to provide a low spin golfball.